Conventional robots are mounted on a stationary base bolted to the floor so that they can withstand the forces and torques applied to the base when the arm carries a payload. Nowadays, with the availability of low-cost high-performance computers, real-time control algorithms can be implemented for mobile-base robots. Base mobility extends the reach of the manipulator arm considerably, and hence increases the size of the robot workspace substantially at a low cost. The base mobility can take different forms and four common implementations are:
(i) Tracked Robots: The robot base is mounted on a platform that can move back and forth along a track installed on the floor. Welding and painting robots are the most common tracked robots; PA1 (ii) Gantry Robots: The robot is mounted on an overhead gantry that provides mobility in two horizontal directions and one vertical direction. These robots can carry very large payloads and can operate where floor space is critical; PA1 (iii) Wheeled Robots: The robot is mounted on a vehicle that can move on wheels. Examples of this class are the microrovers planned for space exploration; PA1 (iv) Compound Robots: The robot base is supported by another robot manipulator bolted to a fixed structure. The inner robot is typically a crane arm used as a crude positioning device. This robot has a large work envelope, slow movement characteristics, a high payload handling capacity, and is often referred to as the "marco" manipulator. The outer robot is a smaller and lighter manipulator that can provide dexterous manipulation with fast and precise movement capability, and is often called the "micro" manipulator. The robot system planned for the Space Station Freedom is a compound macro/micro manipulator. PA1 4,483,407 Iwamoto et al PA1 4,590,578 Barto Jr. et al PA1 4,702,661 Bisiach PA1 4,706,204 Hattori PA1 4,804,897 Gordon et al PA1 4,853,603 Onoue et al PA1 4,894,595 Sogawa et al PA1 4,937,511 Herndon et al PA1 4,954,762 Miyake et al PA1 5,021,878 Lang PA1 5,031,109 Gloton PA1 5,155,423 Karlen et al PA1 5,156,513 Galan et al PA1 5,157,315 Miyake et al PA1 5,245,263 Tsai et al PA1 5,260,629 Ioi et al
A search of the prior art has revealed the following U.S. Pat. Nos.:
Of the aforementioned patents, the following appear to be relevant:
U.S. Pat. No. 4,590,578 to Barto Jr. et al is directed to an off-line programmable robot, As FIG. 1 shows, robot 10 having articulated arm 12 is fixed on base 22 which, in turn, is mounted on carriage track 40. A single controller, controller 70, controls both the motion of articulated arm 12 about the six axes 14-19, as well as the movement of the base along a seventh axis 42. In order to maintain accuracy in the location of the machine operations on workpiece 34, controller 70 performs "on the fly" determination of the positional relationships between workpiece 34, fixture 36, touch blocks 43-48, track 40, and robot 10.
U.S. Pat. No. 4,954,762 to Miyake et al is directed to a method and apparatus by which the tracking path of an industrial robot relative to other movable elements is controlled. As FIG. 1 shows, robot 1 is mounted on travelling stand vehicle 2 which is movably mounted on stand base 20. A single microprocessor 61 controls the relative orientation of robot arms 10, 11, 12 and 13 which manipulate welding torch 30; travelling stand vehicle 2; and positioner 4 which holds working object 5. Thus, manipulation of robot 1 and its translational movement are under real time coordinated control, as in the disclosed concept.
U.S. Pat. No. 4,894,595 to Sogawa et al is directed to an industrial robot. As FIG. 1 shows, the industrial robot comprises arm arrangement 1 supported on base 3 with drive units 3X, 3Y and 3Z, defining the mechanical interface between the two. Control unit 5 which includes command section 7 and position designation device 6, as shown in FIG. 2, coordinates the movement of robot arm 1, hand 2, and driven members 4A and 4B about their respective axes of motion. Here again, one controller commands the translational and manipulator movements of a robot arm.
U.S. Pat. No. 5,260,629 to Ioi et al is directed to a control device for a robot in an inertial coordinate system. As FIG. 2 diagrams, the control device operates on a system comprising robot 1 with a number of arms 3 and body 2, each of which have multiple degrees of freedom. The approach essentially is to measure the velocity or acceleration of robot body 2 with accelerometer 14 contained therein, then to add that measured parameter to a desired value expressed in absolute coordinates so as to command the robot arm to follow any desired path within that absolute coordinate system. Thus, translation of robot body 2 and the movement of robot arm 1 are coordinated, within a common coordinate system.
U.S. Pat. No. 5,156,513 to Galan et al is directed to an apparatus for handling clothes on hangers. As shown in FIG. 1, the apparatus is basically an auto-guided vehicle with manipulators for the controlled handling of clothes on a hanger. The relevance to your concept here is that control of auto-guided vehicle 2, article arm 4, horizontal arm 5, and clamp 6 is provided by a common onboard computer. Accordingly, the DC motors controlling each of these components are appropriately turned on and off by that onboard computer.
In recent years, there has been a growing interest in the analysis and control of mobile robots. Carriker, Khosla, and Krogh formulate the coordination of mobility and manipulation as a nonlinear optimization problem. A general cost function for point-to-point motion in Cartesian space is defined and is minimized using a simulated annealing method. Pin and Culioli define a weighted multi-criteria cost function which is then optimized using Newton's algorithm. Lin and Lewis describe a decentralized robust controller for a mobile robot by considering the base and the robot as two separate subsystems. Finally, Hootsmans and Dubowsky develop an extended Jacobian transpose control method to compensate for dynamic interactions between the manipulator and the base.
The present invention departs from the previous approaches by treating the base degrees-of-mobility equally with the arm degrees-of-manipulation. Configuration control formalism is then used to augment the basic task of end-effector motion by a set of user-defined additional tasks in order to exploit the redundancy introduced by the base mobility. The mobility and manipulation degrees-of-freedom both contribute to the execution of the basic and additional tasks. This approach is simple and computationally efficient and is therefore well-suited for on-line control of mobile robots.